Telephone system



March 31, 1936. T. F. cRocKE TELEPHONE SYSTEM Filed oct. 1, 1934Patented Mar. 3l, 1936 UNTED STATS lPATENT QFFICE 2,035,594 v TELEPHONESYSTEM Application October 1, 1934, Serial No. 746,365

20 Claims. (Cl. 179-18) This invention relates in general to telephonesystems but more particularly to small private automatic telephonesystems, and the principal object of the invention is to design a small,eni- '5 cient and economical telephone system for use in industrialorganizations, schools, residences, and such.

A further object is to provide a small telephone system having a singlecommon talking trunk,

10 with the telephone connections arranged on a secret service basis. Inaccordance with the foregoing object, a particular feature of theinvention is directed to the means whereby certain oi the telephones maybe arranged for right-of-way 1D service so as to at any time connectwith an already established connection.

Another object of the invention is to provide a system wherein a maximumof ten lines is provided andin which only a single conversation be- 20tween any two lines at a time can be had. A particular feature concernsthe means whereby a single individual line relay serves as a connectinglink for each telephone, together with a single motion switch forselecting the called line. 25 A further feature concerns an arrangementfor indicating to a calling telephone the busy or idle condition of thecommon trunk.

The above objects and feature together with others not specificallyenumerated will be pointed 30 out more in detail hereinafter inconnection with the accompanying drawing which shows by means of theusual circuit diagram a preferred embodiment of the invention.

Referring to the drawing, in the upper portion of the sheet fourtelephones are shown, No. 10, No. 20, No. 90, and No. i), the remainingsix telephones off the system not being shown. Each telephone hasassociated with it a line relay, for example, line relay associated withtelephone No. 10. At the right-hand side of the drawing a number ofcommon relays are shown, while at the lower left-hand corner a rotaryswitch S is diagrammatically shown. The contacts of the upper bank areconnected to wires extending to the call signals or ringers of each ofthe telephones while the bank contacts of the lower set are connected toleads extending to contacts of the common cut-01T relay il! and also theline so relays. The switch S is mechanically constructed i-n well knownmanner and comprises essentially' a stepping magnet I2, which upon eachattraction of its armature engages a pawl with a ratchet which is on theshaft upon which the wipers 3l 55 and 32 are supported so as to rotatethese Wipers step by step in a forward direction over theircorresponding set of bank contacts. The operation of the release magnetI I withdraws the pawl from the ratchet and under control o-f atensioned spring the Wipers are restored to normal position. 5 A set ofoff-normal contacts I3 and i4 are actuated to close immediately that theswitch wipers are stepped off-normal.

In describing the detailed operation of the system it will be assumedthat the system as disl0 closed is installed in an industrialorganization and that each of the ten telephones are scatteredthroughout the premises. All of the connection equipment including therelays and the switch S may be suitably mounted in a small cabinet at l5some centrally located position, and each of the telephones will havethree wires extending from the equipment to the telephones, two of theline wires extending to the associated line relay while the third wireextends to the bank of the switch S.

Assume now that the telephone No. l0 desires to establish a connectionwith telephone No. 00. The removal of the receiver R from the switchhookS at telephone No. l0 establishes a circuit path extending from batterythrough the winding of line relay 5, lback contact and armature E oi theaforesaid relay, line conductor 22, normally closed contacts of theimpulse sender or calling device D, transmitter T, receiver R contactsof the switchhook S, back over line conductor 23, armature 8 and itsback contact, conductor 9, to ground on the back Contact of armature 12of the cut-01T relay l0. Line relay 5 energizes over this circuit pathand operates its armatures 6, 'l and 8. At the front contacts ofarmatures 8 and 35 8 the line conductors 22 and 23 are connecteddirectly to the common trunk 32 and 33 extending to the windings of linerelay d5 and battery and ground respectively. At the back contacts ofarmatures 6 and 8 the original energizing cir- 40 cuit of relay 5 isopened and a locking circuit for it is completed extending from batterythrough winding of line relay 5, front contact and armature 1, commonlocking conductor 3|, through the Winding of slow rel-ease relay 15, toarmature 'll and its back contact to ground. The front contact ofarmature 1 closes first before the original energizing circuit for relay5 is opened at the back contacts of armatures 6 and 8.

Relay 'l5 energizes in series with line relay 5 and at its front contactand armature 16 connects ground through the winding of slow-to-energizerelay 'l0 to battery. 'I'his relay slowly energizes but does notimmediately operate its armature. 55

Line relay 45 having its circuit closed through the upper and lowerwindings energizes and closes ground on armature 4I fo-r a purpose whichWill be pointed out later on, while at the impulsing armature 42 itconnects ground to the front contact and to the winding ofslow-to-release relay 50 to battery. R/elay 5D, upon operating, atarmature 52 and its back contact disconnects ground from conductor 21,while at the front contact of this armature ground is connected toconductor 26, a branch of which extends through the winding of relay 15.At front contact and armature I a circuit :for relay 55 is prepared.During ground as just described on armature 52 to hold relay 15 and theline relay 5 energized in series.

As a further result of the operation of relay it operates its remainingten armatures including armatures 12, 13, 14 and 84 to disconnect groundfrom the back contacts of these armatures extending over leads 9, 89,48, etc., to armatures 8, I8, intermediate similar armatures, armatures38 and armature 48, so thatthis ground is disconnected from all thelines in the system and Will prevent the associated line relays fromoperating in case their telephones attempt to initiate a call at thetime relay 5 is operated in initiating a call from its associatedtelephone No. 10. It will be seen that as long as relay 10 is.energizedrno other telephone can initiate a call or connect to thecommon trunk 32 and 33 except in certain instances which willhereinafter be pointed out.

As a further result of the energization of line relay 45 it closesground from its front contact to its armature 4I over back contact andarmature 69, back contact and armature B1, through the winding ofringing relay 65 to battery. Relay 65, upon energizing, rst closes itsfront contact on armature 66 and completes a circuit extending fromgrounded front contact and armature 4I, front contact and armature 66,high resistance 53, line conductor 32, through the upper Winding of linerelay 45 and battery. At the back Contact of armature $1 theenergizingcircuit of relay 65 is opened and this relay retracts its armatures. Asarmature 4I in relay 45 is still operated the relay immediately.energizes again. Relay 65, therefore, energizing and deenergizesrapidly in succession in the manner of a buzzer and rapidly opens andcloses its contacts 66. This action generates a tone called the dialtone in the line conductor 32 which does not alect the operation of linerelay 45, because of the high resistance of resistance 53. Thetonegenerated is, however, transmitted over the line conductor 32 to thetransmitter T and receiver R and informs the person at the callingtelephone No. 10 that the common trunk is idle and not in use by othertelephones. At armature 68 of relay 65 battery is connected to its frontcontact without eiect at this time, however.

The person at telephone No. 10 hearing the dial tone generated by relay65 and being aware that telephone, which in this instance is 0,corresponding to ten impulses. The line relay 45 deenergizes, responsiveto the first opening of the impulse springs D over thelline circuitcomprising conductors 22 and 23, 32 and 33. Relays 5U and 55, beingrendered slow to release due to the copper slug on their heel endsremain energized throughout the series of impulses. A circuit is nowclosed when the line relay 45 falls back, from ground on armature 42 andits back contact, armature 5I and its front contact, through the windingof slow release relay 55 tobattery. A branch of the energizing circuitof relay 55 extends by Way of back contact and armature 6I, conductor29, through the winding of stepping magnet I2 to battery, of the switchS, thereby energizing this stepping magnet. The stepping magnet I2, uponenergizing, operates its pawl to rotate the wipers 3I and 32 in aforward direction as indicated from the first to the second set of bankcontacts. At the same time the wipers are rotated the off normalcontacts I3 and I4 close.

As a further, result of the energization of relay 55 it closes its frontcontact and armature 56 thereby extending ground from front contact andarmature 4I, through the winding of relay 65 to battery, thereby holdingthis relay energized so it will no longer vibrate its armature and frontcontact 66, and consequently disconnects the dial tone from the lineconductor 32. At front contact of armature 51 relay 55 closes a furtherpoint and a locking circuit for relay 65 through its front contact andarmature 61 through the relay to battery; and by Way of conductor 28closed oir-normal contacts I3, to front contact and armature 52 andground. This circuit therefore holds relay 65 operated independent ofground on armature 4I which is connected and disconnected by subsequentenergizations and deenergizations of line relay 45 due to the impulses.At armature 68 relay 65 prepares a ringing circuit which will be lateron pointed out.

After the rst impulse from the calling device D at telephone No. 10 theremaining series of impulses operate line relay 45 to attract andretract its armatures rapidly in succession, relays 55 and 55 remainingenergized for the duration of the impulses and each impulse beingtransmitted from the impulse contacts at armature 42 by way of armatures5I 6I and conductor 29 to the stepping magnet I2, thereby rotating thewipers 3| and 32 across the bank contacts of the switch S.

After the first series of ten impulses have been transmittedby thecalling device D relay 45 again remains energized when it comes to restand armature 42 maintains relay 50 in the same position. At the backcontact of armature 42, however, the circuit for relay 55 is permanentlyopened and after a short interval this relay deenergizes and releasesits armatures. At armature 56 relay 55 opens the original holdingcircuit of relay 65, While at armature 51 it opens the locking circuitfor this relay and relay 65 consequently deenergizes and retracts itsarmatures. At the back contact of armature 51 relay 55 completes acircuit for relay 60 extending from battery through the winding of thisrelay, back contact and armature 51, conductor 28, closed offnormalsprings I3, conductor 26, front contact and armature 52 of relay 5i) toground. Relay 60 consequently energizes and at its front contact andarmature B2 completes a lockingcircuit for itself independent of theback contactvof armature 51, and at armature 5I and its back Contactopens the circuit of the stepping magnet I2; at front contact andarmature 64 it closes a point in the ringing circuit which, however, atthis time is open by relay 65 at its armature 68; at front Contact andarmature 63 it connects ground to conductor 33 which extends. to wiper32 and bank contact I6 upon which it is now resting, to conductor 49This ground connection is in substitution for that which originally wasdisconnected from this conductor 49 at armature 84 by the operation ofrelay 10.

The second digit of the called telephone number is now dialled. Thisdigit 0, it will be noted, is the same for each of the telephones in thesystem, and constitutes the ringing digit; the first digit in eachinstance selecting the telephone which is being called. The operation ofthey calling device D at telephone No. 10 in accordance with the digit 0transmits ten impulses over the line conductors 32 and 33 to energizeand deenergize line relay 45 a corresponding number of times. At the rstdeenergization of line relay 45 responsive to the first impulse itcompletes a circuit again from grounded armature 42 and its backcontact, armature and its front contact, to relay 55 and battery. At thefront contact and armature 56 it closes the circuit for relay 65 fromground on armature 4| responsive to the rst impulse, so that this relayimmediately energizes. At front contact of armature 51 relay 55 closes alocking circuit for relay 65 by way of its armature 61, so that itremains permanently energized during the series of impulses independentof the ground on armature 4| which vibrates in synchronism with theenergization and deenergization of line relay 45. Relay 66 at this timebeing locked energized over armature and front contact 62, impulses nolonger are transmitted over back contact and armature 6| to the steppingmagnet I2 due to the opening of this armature.

Due to the energization of relay 65 battery is connected through theresistance 58, front contact and armature 68, front contact and armature64, over conductor 34, wiper 3| and the tenth bank contact upon which itis now resting, ringing conductor 83 extending to telephone No. 00through the ringer B, at telephone 00, normally closed switchhookcontacts S, line conductor 86, armature 48 and its back Contact,conductor 49, extending to bank contact No. 10, wiper 32 which is nowresting on this bank contact, conductor 33. armature 63 and its frontcontact to ground. The circuit above pointed out actuates the ringer Bto audibly signal the person at this telephone.

After the last impulse has been transmitted to relay 45 it again becomespermanently energized and holds relay 5D operated. At the back contactof armature 42 relay 55 has its circuit opened so that when itdeenergizes it opens the original energizing circuit of relay 65, whileat armature 51 it opens the locking circuit for this relay and relay 65consequently deenergizes and retracts its armatures. Relay 60, however,remains locked energized over front contact and armature 62 to ground onarmature 52 and its front contact, and at armature 69 prevents theenergization of relay 65 again from armature 4|. Should the person attelephone station No. 00 neglect to answer his telephone immediately,his ringing device B may again be actuated, by the person at telephoneNo. again dialling the digit 0. This re` sults in the energization or"relays 45, 50, 55 and 65, as has been pointed out, to again actuate theringing device. This dialling of the digit 0 may be repeated as manytimes as desirable or until the person at the called telephone answersand at the end of each series of impulses relays 45 and 56. remainenergized while relays 55 and 65 are deenergized.,

The removal of the receiver R from the switchhook S disconnects theringing dev-ice B and'` prevents its further operation.v At the sametime the front contacts of the switchhook SV close av loopy circuitextending through the receiver R transmitter T, impulse springs D overline conductors 86 and 81, back contact of armature 46, through thewinding of line relay 40 to battery and the ground connected toconductor 4.6 to back contact and armature 48. The line relay 40energizes` over this loop circuit and at its front contact and armature41 completes a locking circuit for itself over conductor 3| through thelwinding of relay to the front Contact andarmature 52 and ground. At thefront contact of armatures 46 and 48 the line conductors 86 and 81 areoonnected directly to the common trunk 32 and 33 to which lineconductors 22 and 23 of the telephone No. 10 are connected by armatures6 and 8 of relay5. The telephones No. 10 and No. 00 are both nowconnected directly to the common trunk 32 and 33 and both parties maynow converse, battery current for talking purposes being furnishedthrough the windings oi the line relay 45.

Should it occur that during the time that telephones No. 10 and No. 00are engaged in a connection that another telephone, for example, No. 20,desires to establish a call, the connection will be prevented from beingmade or the person from listening in on an existing connection due tothe fact that the energizing circuit for line relaiT Hl of telephone No.will be open due to the energization of relay 10, at armature 88. RelayI0, therefore, cannot energize and because of the absence of dial tonefrom relay 65 the person at telephone No. 20 will be aware that thecommon trunk 32 and 33 is in use and that he must wait until the trunkreturns to normal before attempting to establish a connection withanother telephone. From the foregoing it is seen that all conversationsare on a secret service basis, asV no other station can connect to thecommon trunk as long as it is in use,V except as will hereinafter bepointed out.

In certain instances it may be desirable that certain telephones used bya supervisor or an executive, for example, be arranged so that they mayat all times have access to the common trunks 32 and 33 and also thatthey may be enabled to cut in onto an established connection alreadyexisting on the common trunk between two other telephones. To providefor this rightof-way service certain of the telephones,- for exampletelephone No. 60 and telephone No. 90 are arranged for this service. Astrap 43 isA connected around the contactsr 13 of cut-off relay 10 fortelephone No. 60 and the strap 44 around armature contacts 14 fortelephone No. 90. With this arrangement should telephones No. l0l andNo. 00 be engaged in a connection over common trunk 32 and 33 andtelephone No. 90 desires to make a connection, the removal of thereceiver R from the switchhook at telephone No. 90 completes the circuitfor line relay 35 by way of conductor 89, the strap 44 around armature,14 and its back contact to ground. Therefore the line relay 35 willbecome energized to close its front contact onto armatures 36 and 38 andconnect the telephone No. 90 direct to the common conductor 32 and 33.This circuit for relay' 35 is rendered available as pointed out in spiteof the fact that relay 16 is operated, and the arma,- ture 14 is openfrom its grounded back contact. The telephone No. 90 is thereforedirectly con` nected onto the commontrunk 32 and 33 and can inform theparties already engaged in a conversation that he desires the use of thecommon trunk or request them to hang up their receivers or listen in onthe conversation. From the foregoing it is seen that any telephonedesired may be equippedV with the straps such as 43 and 44, it being asimple matter to provide these, or to disconnect them from any telephonein the system, thereby rendering this service extremely flexible. If theperson at telephone No. desires to have the common trunk line cleared,the telephones No. 10 and No. O0 must be restored to normal by thereplacement of their receivers, as well as that of telephone No. 90, inorder that all of the equipment may be in its normal position so thattelephone No. 90 can establish the connection with the other desiredtelephone which it is to call.

After the telephonesl No.' 10 and-No. 00 hav finished their conversationand the last oneA of them to hang up replaces the receiver R upon theswitchhook S, the circuit extending over common trunk 32 and 33 to linerelay 45 is interrupted at the front contact of the last switchhook.Line relay 45 consequently deenergizes and retracts its armature 42.Ground is thereby connected from the front contact of this armature'from relay 50 and this relay upon slowly deenergizing finally restoresits armatures 5I and 52. At the front contact and armature 52 ground isdisconnected from conductor 26 extending through relay 'I5 to conductor3|. 'Ihis ground, it will be recalled, extends over the conductor 3l toarmature 41 and the front contact of line lrelay 40, and to armature Iand its front contact on line relay 5. These line relays thereforedeenergize and restore their respective'armatures. Line relay 5 atarmatures 6 and disconnects the telephone No. 10 from the common trunk32 and 33, while line relay 40 at armatures 45 and 48 disconnects thetelephone No. 00 from this trunk. Slow release relay 'I5 after aninterval disconnects ground from the front conducto-r and armature 'I6to interrupt the circuit of relay '10. This relay after a short intervalcloses its ten armatures on to their back contacts and`connects groundto all the conductors extending to the line relays, rendering the systemavailable for other calls. As a further resultof the retraction ofarmature 52 of relay 50 ground is disconnected frorn conductor 2Bextending'by Way of off-normal contact I3 to conductor 23, armature 62and its front contact, which maintains relay BG energized. RelaySithereupon deenergizes and restores its armatures. At the back contactof armature 52 ground is' connected to this armature and over conductorl21 through off-normal contacts I4, and through the winding of releasemagnet l I to battery. Releasel magnet II, upon energizing, withdrawsthe pawl holding wipers 3I and 32 on the bank contact No. 10 and underthe action of a tensionedcoil spring, the wipers are restored to normalYposition onto their rst set of bank contacts. Shortly before thesewipers reach this position the off normal contacts I3 and I4 are opened,resultingin contacts I4 opening the circuit of release magnet II whichthereupon restores. All relays and apparatus of the system are nowintheir normal condition, ready to receive another call.

Having described the invention, what is new and is desired to beprotected by Letters Patent ,will be set Aforth in the following claims.Si Y What is claimed is:

1. In aV telephone system, a plurality of lines, a line relay individualto each of said lines, means responsive to a call from any of said linesfor operating its associated line relay, means responsive to theoperation of said line relay for preventing the operation of all of saidother line relays, a step-by-step switch connected to said line relays,land means controlled over the calling line for operating saidstep-by-step switch-to select for operation only the line relay of thecalled line.

2. In a telephone system, a plurality of lines, a line relay individualto each of said lines, a 'cut-off relay controlling the energizingcircuit of said line relays means responsive to a call from a line foroperating its associated line relay and for operating said cut-oil relayto disconnect the energizing circuits of all of said other line relays,a step-by-step switch, means controlled over said calling line' foroperating said step-bystep switch to connect with the line relay of thecalled line, and means for operating said called line relay through saidstep-by-step switch independent of said cut-off relay.

3. In a vtelephone system, a plurality of telephone lines each having anindividual line relay Vassociated with it, a cut-ofi" relay controllingthe circuits of all of said line relays, means responsive to theinitiating of a call from any line for operating its associated linerelay and for operating said common cut-01T relay to disconnect theenergizing circuit of all of said line relays including the line relayof the called line, a stepby-step switch operated over the calling lineto select the line relay of the called line, and means for 'operatingthe called line relay over said switch over a circuit path independentof the control by said cut-o-i relay.

4. In atelephone system, telephone lines, a line relay individual toeach of said telephone lines, a common cut-off relay controlling thecircuits to each of said line relays, means responsive to a call fromany line for operating its associated line relay and for operating saidcut-off relay to disconnect all of said other line relays to preventtheir' operation, and means on said common cutoff relay for permittingthe operation of only certain of said line relays.

5. In a telephone system, a plurality of tele- Y phone lines, a linerelay individual to each of said telephone lines, a cut-off relay commonto all of said lineV4 relays and controlling their energizing circuits,certain of said line relays controlled independent of said commoncut-olif relay, means responsive to the initiation of a call from anyline for operating its associated line relay, and for operating saidcommon cut-off relay to disconnect all energizing circuits from all theline relays except certain ones, means controlled over the calling linefor operating the line relay of` the called-line over a circuitindependent of said common cut-oli relay to establish a connectionbetween the calling and the called line, and means responsive to a callfrom any of said certain lines for operating its associated line relayto connect directly to said established connection independent of saidcommon cut-off relay.

6. In a telephone system, a plurality of lines, a line relay for each ofsaid lines, a common cut-off relay having a contact for controlling theP' circuit for each of said line relays, means responsive to a call fromany line for operating its associated line relay and for operating saidcut-off relay to operate its contacts to disconnect the circuits of allother of said line relays except the calling line, and means on certainof said cut-off relay contacts for operating a line relay correspondingto the contact independent of said contact.

7. In a telephone system, a plurality of lines, a line relay individualto each of said lines, a common trunk connected to contacts of each ofsaid line relays, mea-ns responsive to the initiation of a call from oneof said lines to another of said lines for operating the line relays ofthe calling line and of the called line to connect said lines to saidtrunk over the contacts of the operated line relays, and other meansresponsive to said call for preventing the operation of all other ofsaid line relays.

8. In a telephone system, a plurality of lines, a line relay individualto each of said lines, a common trunk line connected to contacts ofleach of said line relays, means responsive to the initiation of a callfrom any line to another line for operating the called and calling linerelays to connect the common trunk line through their associatedcontacts to the calling and called lines, a common cut-oi relay operatedresponsive to the initiation of a call, and contacts controlled by saidcommon cut-oi relay for disconnecting all other line relays from saidtrunk line except the calling and called line relays.

9. In a telephone system, a plurality of telephone lines, aline relayindividual to each of said lines, a common talking trunk line connectedto each of said line relays, a common cut-01T relay controlling thecircuits of said line relays, means responsive to the initiation of acall from any line for operating its associated line relay and foroperating the common cut-off relay to disconnect all of said other linerelays from operation, means responsive to the operation of said callingline relay for connecting the calling telephone to said common talkingtrunk, means controlled from said calling line for operating the linerelay of the called line independent of said common cut-01T relay, andconnections on said common cut-oi relay for permitting the operation ofonly certain of said line relays independent of said cut-off relays sothat certain line relays can operate and connect their associatedtelephones directly to said common talking trunk at a time when saidtrunk is engaged in a connection between a calling and called line.

l0. In a telephone system, a plurality of lines each having a telephonesubstation thereon including an automatic calling device, a step-bystepswitch, means responsive to a digit dialled by a calling telephone foroperating said step-bystep switch to connect with a called line, andmeans responsive to a second digit dialled by said calling telephone forsignalling said called telephone over said switch.

1l. In a telephone system, a plurality ci substations each having acalling device thereat, a step-by-step switch including a pair ofwipers, means responsive to a digit dialled by a calling substation foroperating said step-by-step switch to connect one of its wipers With thecalled telephone, and means responsive to a second digit dialled by saidcalling telephone for signalling said called telephone over the other ofsaid switch wipers.

12. In a telephone system, a plurality of substations each having acalling device, a step-bystep switch, means responsive to a digitdialled from a calling telephone for operating said stepby-step switch,said step-by-step switch having a pair of wipers, a rst one of saidwipers operated responsive to said digit to connect with the calledtelephone substation, the second one of said wipers operated to selectthe signalling device at the called station, means responsive to asecond digit dialled from said calling substation for operating thesignalling device at the called station over said second wiper, and saidlast means responsive to dialling additional digits to operate saidcalled signalling device over said second wiper.

13. In a telephone system, a plurality of lines, a line relay individualtoeach of said lines, a common talking trunk connected to each of saidline relays, means responsive to the initiation of a call from any linefor operating its associated line relay and the line relay of the calledline to connect said calling and called telephones through theirassociated line relays to said common talking trunk, a common cut-offrelay operated responsive to the initiation of a call for disconnectingall other line relays from said common talking trunk, and means .forconnecting a tone to said common trunk to indicate to said calling linethat said common trunk is not engaged in a connection.

14. 'In an automatic telephone system, telephone lines each having asubstation connected thereto including a calling device, a line relayindividual to each of said lines, a common talking trunk connected toall of said line relays, a cutoff relay common to all of said linerelays and controlling the circuits thereof, a step-by-step switchhaving a pair of wipers, one of said wipers having its bank contactsconnected to said line relays while the other wiper has its bankcontacts connected to a signalling device at each substation, meansresponsive to the initiation of a call from any substation for operatingits associated line relay and said common cut-off relay, meansresponsive to the operation of said cut-off relay for disconnecting saidother line relays from operation, means responsive to a rst digitdialled by said calling line for operating said step-bystep switch torotate its wipers, the first of said wipers operated to a connectionwith a called line relay to operate the same independent of said commoncut-off relay, said calling line relay and said called relay operatingto connect said lines to said common talking trunk, the second of saidwipers operated to connect with said signalling device at said calledsubstation, and means responsive to the dialling of a second andsubsequent digit for repeatedly operating the signalling device at saidcalled substation.-

15. In a telephone system, a plurality of lines, s-ubstations on each ofsaid lines each having a signalling device, a step-by-step switch havinga pair of Wipers, a common cut-eff relay for all of said lines, meansresponsive to the initiation of a call from any line for operating saidcut-01T relay to prevent any other line from initiating a call, meansresponsive to digits transmitted from said callingV station foroperating said step-bystep switch, the rst wiper of said switch operatedto select the called substation telephone and render it operativeindependent of said common cut-01T relay, the second of said wipersoperated to select the signalling device at the called telephone, andmeans responsive to a second digit dialled by said calling telephone foroperating said signalling device over said wiper.

16. In a telephone system, a plurality of lines, a line relay individualto each of said lines, a common talking trunk common to and connected toeach of said line relays, means responsive to the initiation of a callfrom a calling telephone for operating its line relay to connect saidline with said common talking trunk, a relay operated responsive to theseizure of said trunk by said line relay to transmit a tone over saidtrunk to said calling telephone to indicate that the trunk is in idlecondition, means controlled from said calling telephone for preparingthe establishment of a connection over said common talking trunk With acalled line by selectively preparing only the called line relay foroperation, and means controlled from said calling line for signallingsaid called line.

17. In a telephone system, a plurality of telephone lines, a trunk linecommon to all of said lines, means responsive to the initiation of acall from any of said lines for connecting said line to said trunk line,a relay, means responsive to the connection of the line with said trunkline for operating said relay to transmit a tone over said trunk line tosaid calling line to indicate the idle or busy condition of said trunkline, means controlled by said calling line over said trunk line forestablishing a connection With another of said telephone lines, andmeans controlled from said calling telephone line for operating saidrelay to signal said called line over said common trunk.

18. In a telephone system, a plurality of lines, a common trunk line forall of said lines, a relay connected to said trunk line, meansco-ntrolled from a calling station for operating said relay in onemanner to indicate to the calling line that said common trunk is notbusy, means controlled from said calling line in another manner tooperate said relay in a diierent manner, and means responsive to thelast operation of said relay for signaling the called line.

19. In a telephone system, a plurality of lines, a line relay individualto each line, a cut-off relay common to all said lines and operated incombination with any one of said line relays in response to theinitiation of a call on any one of .said lines, a contact on said cut-orelay for each line relay, an automatic switch operable from any one ofsaid lines, an individual connection from said switch to each line, arst operating circuit for each line relay including its individualcontact on said cut-off relay, and a second operating circuit for eachline relay including the loop of its corresponding line and thecorresponding individual switch connection.

20. In a telephone system, a plurality of lines, a line relay individualto each line, a cut-olf relay common to all said lines, an individualcontact on said cut-off relay for each line, an individual connectionfor each line connected in multiple with its corresponding cut-ofi relaycontact, a rst operating circuit for each line relay including itsindividual contact on said cut-off relay, and a second operating circuitfor each line relay including the loop of its corresponding line and thecorrespon-ding individual connection.

THOMAS F. CROCKER.

